aac895409a
Add prng(9) as a replacement for random(9) in the kernel.
There are two major differences from random(9) and random(3):
- General prng(9) APIs (prng32(9), etc) do not guarantee an
implementation or particular sequence; they should not be used for
repeatable simulations.
- However, specific named API families are also exposed (for now: PCG),
and those are expected to be repeatable (when so-guaranteed by the named
algorithm).
Some minor differences from random(3) and earlier random(9):
- PRNG state for the general prng(9) APIs is per-CPU; this eliminates
contention on PRNG state in SMP workloads. Each PCPU generator in an
SMP system produces a unique sequence.
- Better statistical properties than the Park-Miller ("minstd") PRNG
(longer period, uniform distribution in all bits, passes
BigCrush/PractRand analysis).
- Faster than Park-Miller ("minstd") PRNG -- no division is required to
step PCG-family PRNGs.
For now, random(9) becomes a thin shim around prng32(). Eventually I
would like to mechanically switch consumers over to the explicit API.
Reviewed by: kib, markj (previous version both)
Discussed with: markm
Differential Revision: https://reviews.freebsd.org/D25916
132 lines
3.4 KiB
C
132 lines
3.4 KiB
C
/*-
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* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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*
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* Copyright 2020 Conrad Meyer <cem@FreeBSD.org>. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/kernel.h>
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#include <sys/pcpu.h>
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#include <sys/prng.h>
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#include <sys/smp.h>
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#include <sys/systm.h>
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#if !PCG_HAS_128BIT_OPS
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/* On 32-bit platforms, gang together two 32-bit generators. */
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typedef struct {
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pcg32u_random_t states[2];
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} pcg64u_random_t;
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static inline void
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pcg64u_srandom_r(pcg64u_random_t *state64, uint64_t seed)
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{
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pcg32u_srandom_r(&state64->states[0], seed);
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pcg32u_srandom_r(&state64->states[1], seed);
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}
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static inline uint64_t
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pcg64u_random_r(pcg64u_random_t *state64)
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{
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return ((((uint64_t)pcg32u_random_r(&state64->states[0])) << 32) |
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pcg32u_random_r(&state64->states[1]));
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}
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static inline uint64_t
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pcg64u_boundedrand_r(pcg64u_random_t *state64, uint64_t bound)
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{
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uint64_t threshold = -bound % bound;
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for (;;) {
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uint64_t r = pcg64u_random_r(state64);
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if (r >= threshold)
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return (r % bound);
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}
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}
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#endif
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DPCPU_DEFINE_STATIC(pcg32u_random_t, pcpu_prng32_state);
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DPCPU_DEFINE_STATIC(pcg64u_random_t, pcpu_prng64_state);
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static void
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prng_init(void *dummy __unused)
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{
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pcg32u_random_t *state;
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pcg64u_random_t *state64;
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int i;
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CPU_FOREACH(i) {
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state = DPCPU_ID_PTR(i, pcpu_prng32_state);
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pcg32u_srandom_r(state, 1);
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state64 = DPCPU_ID_PTR(i, pcpu_prng64_state);
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pcg64u_srandom_r(state64, 1);
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}
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}
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SYSINIT(prng_init, SI_SUB_CPU, SI_ORDER_ANY, prng_init, NULL);
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uint32_t
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prng32(void)
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{
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uint32_t r;
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critical_enter();
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r = pcg32u_random_r(DPCPU_PTR(pcpu_prng32_state));
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critical_exit();
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return (r);
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}
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uint32_t
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prng32_bounded(uint32_t bound)
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{
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uint32_t r;
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critical_enter();
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r = pcg32u_boundedrand_r(DPCPU_PTR(pcpu_prng32_state), bound);
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critical_exit();
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return (r);
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}
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uint64_t
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prng64(void)
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{
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uint64_t r;
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critical_enter();
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r = pcg64u_random_r(DPCPU_PTR(pcpu_prng64_state));
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critical_exit();
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return (r);
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}
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uint64_t
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prng64_bounded(uint64_t bound)
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{
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uint64_t r;
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critical_enter();
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r = pcg64u_boundedrand_r(DPCPU_PTR(pcpu_prng64_state), bound);
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critical_exit();
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return (r);
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}
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